Some airfoils, particularly large ones, are provided with inserts during manufacturing. An airfoil may have one or more inserts, depending of the design. Each insert is located in a corresponding internal cavity of the airfoil core.
The presence of one or more inserts inside an airfoil offers many advantages. However, there are some drawbacks as well. One of them is that at the location of the insert, pedestals or ribs can no longer be used for interconnecting the internal surfaces of opposite sidewalls. These interconnections help maintain the overall rigidity of both sidewalls, thereby preventing or reducing cracking because of the deflection of the sidewalls. Cracking is also due in part to thermal variations, as the skin of the airfoil is exposed to the hot gas path, and the rib-pedestals are relatively cooler because of the cooling air circulating therein. Zones of relatively high mechanical stresses can occur in one or more sidewalls, particularly at a junction between a rib and a spanning portion of one of the sidewalls adjacent to the insert, or at a junction between a cooling pedestal and a spanning portion of one of the sidewalls adjacent to the insert.
Accordingly, there is a need to mitigate the problem of cracking at zones of high mechanical stresses in the sidewalls of airfoils.